Fractal device for mixing and reactor applications

ABSTRACT

Two or more independent and offset fluid transporting fractals allow the scaling and intermingling of two or more fluids separately and simultaneously prior to contacting the fluids with one another. The device provides rapid and homogeneous mixing and/or reaction.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/291,769, filed May 17, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The instant invention relates to mixing and reactor equipment.More specifically the invention is directed to equipment for mixing andreacting one or more fluids. The invention finds application in singleas well as multi-phase environments.

[0004] 2. State of the Art

[0005] Many fluid processes benefit from efficient mixing. Nearly allconventional art mixing equipment, such as blenders, impellers, staticmixers, and impinging devices, scale and intermingle the fluids to bemixed while the fluids are in actual contact with one another. Thisapproach can result in the creation of a variety of inhomogenietieswithin the body of the fluid mixture. Such inhomogenieties may beharmful to the process of mixing and/or the reactions occurring withinthe body of the fluid. For example, large scale concentration ortemperature inhomogenieties may be produced within the body of the fluidmixture by the use of conventional mixing equipment.

[0006] Additionally, conventional mixing equipment generally relies uponforcing large scale turbulence upon the fluid mixture. Turbulence, inturn, may lead to the formation of eddies within the fluid body which,in many instances, may be as large as the reaction vessel itself. Thepresence of eddies within the fluid body may hamper the proper mixing ofthe fluid and further may disrupt the extent of the reactions occurringwithin the fluid.

[0007] Historically, slight attention has been paid in the art to theuse of engineered fractal mixing as a means of processing fluids. U.S.Pat. No. 5,938,333 is one of the few examples of technical efforts inthis area. In U.S. Pat. No. 5,938,333 a space filling device, which canbe used for low turbulence fluid mixing in a volume, is disclosed. Thisdevice can accomplish volume mixing with very little turbulence and witha high level of homogeneity. Unfortunately, because the device of U.S.Pat. No. 5,938,333 is a space filling mixer, it is not always anappropriate processing device for a given processing requirement.

[0008] Another recent patent which describes the use of fractals todistribute or collect fluids is U.S. Pat. No. 5,354,460 which disclosesa fractal fluid distribution system. PCT/U599/06245 is directed to afractal fluid transporting device. Neither of these references discloseemploying offset fractals to simultaneously and independently scale andintermingle separate fluids for mixing and/or reaction.

BRIEF SUMMARY OF THE INVENTION

[0009] The instant invention provides a method and apparatus for mixingor reacting a fluid mixture wherein one or more of the component fluidsof the mixture are scaled and intermingled prior to their contactinganother component fluid. Central to this method is the use of astructure which includes independent offset fluid transporting fractals.This new structure eliminates large scale eddies by scaling the entireflow of fluids through independent fractals prior to a mixing/reactionof the fluids. Furthermore, the present invention does not mix to avolume and thus the invention provides several new practical industrialopportunities for fractal mixing. This new structure scales and mixesfluid in a manner which is appropriate for flows exiting to or crossingan area (instead of a volume) and is not a space filling fractalconfiguration. We have discovered a number of useful applications whichcan use this different approach. An important example is the use of thisdevice via attachment to a flow-through pipe. This allows simple butefficient pipe flow oriented fluid mixing and reaction. Using thestructure in this manner is beneficial because it allows easyincorporation into existing processing technology. Another industriallyuseful application is attaching the device to the side of a vessel sothat fluids are mixed homogeneously just prior to entering the vessel.Still another useful application is the provision of a surface ofhomogeneously mixed gases for subsequent combustion applications.

[0010] The instant invention is particularly applicable to providingrapid and homogeneous mixing, with or without a reaction occurringbetween the fluids. The invention can also provide controlled mixing andheat transfer simultaneously, for example in order to control thetemperature of a reaction process. Contemplated uses of the inventioninclude the following:

[0011] 1. Mixing two or more fluids rapidly.

[0012] 2. Mixing two or more fluids while controlling temperature.

[0013] 3. Mixing and reacting two or more fluids.

[0014] 4. Mixing and reacting two or more fluids while controllingtemperature.

[0015] 5. Mixing two or more fluids to allow subsequent homogeneousreaction outside the device.

[0016] Further environments wherein the invention may find applicationinclude the following:

[0017] 1. Liquid-liquid mixers.

[0018] 2. Gas-gas mixers.

[0019] 3. Gas-liquid mixers.

[0020] 4. Liquid-liquid reactors.

[0021] 5. Gas-liquid reactors.

[0022] 6. Gas-gas reactors.

[0023] 7. Aerators.

[0024] 8. Carbonators.

[0025] 9. Fluid mixing prior to combustion.

[0026] By using the instant invention, two or more fluids can be rapidlymixed in a homogeneous manner without using mechanical mixing equipment.Turbulence inducing mechanical mixing devices, such as impellers,blenders, impinging devices, etc. are not used. Therefore large scalemixing inhomogeneities can be avoided. Large scale eddies in mixingprocesses can reduce the yield of chemical reactions. This deviceeliminates large scale eddies from the mixing process. Avoidingmechanical mixing can also reduce the amount of energy used. Ordinarymixing processes most commonly result in energy wasted because the largescale turbulence which is forced on the mixing process must eventuallybe dissipated as heat. The device in this invention does not form largescale turbulence or eddies so large scale motion is not dissipated aswasted energy.

[0027] The distribution of fluid properties can be controlled in abeneficial manner using the invention. For example, for a gas mixingwith a liquid, the gas bubble size distribution can be controlled and atthe same time the liquid is also scaled, therefore mass transfercharacteristics are more controlled. Other fluid property distributionswhich can be controlled by this device include fluid velocities,temperature, concentration and eddy size.

[0028] Because fluid property distributions can be more controlledcompared with conventional mixing/reactor equipment, the equipment canbe smaller and more efficient. If desired, the mixing can be rapid andhomogeneous but with very gentle treatment of the fluids. The variousembodiments of the invention can be used as elements in conventionalprocessing. For example, as a rapid mixer in an ordinary pipeline or asan multi-fluid mixer entering a tank or other vessel.

[0029] Unlike nearly all fluid reactors, the various components to bemixed and reacted can all be scaled and intermingled with one anotherprior to contact with one another. This results in a more rapid andhomogeneous reaction. Side reactions caused by large scaleinhomogenieties can be avoided. Furthermore, mixing and reactiontemperature can easily be controlled. Large mixing or reactor tanks canbe completely eliminated since all the fluids to be mixed and/or reactedcan be scaled and intermingled together in this device.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0030]FIG. 1 is a cross sectional view of an offset fractal structure ofthe invention;

[0031]FIG. 2 is a plan view of two fractal distributors illustrated inan offset orientation;

[0032]FIG. 3 is a perspective view of the two fractal distributors ofFIG. 2 in association with a collector;

[0033]FIG. 4 is a top view of a fractal structure in association with apipe element;

[0034]FIG. 5 is a perspective view of the fractal structure of FIG. 5;

[0035]FIG. 6 is a cross sectional view of an alternative embodiment ofthe fractal structure;

[0036]FIG. 7 is a cross sectional view of a further alternativeembodiment of the fractal structure.

[0037]FIG. 8 is a perspective view of yet another alternative embodimentof the fractal structure wherein the structure is not enclosed within acontainment vessel.

DETAILED DESCRIPTION OF THE INVENTION

[0038]FIG. 1 illustrates an embodiment of a fractal structure which inaddition to the offset fractal characteristic of this invention alsoincludes merging and contact channels, a fractal collector and a heatexchange enclosure. This embodiment is useful as a processing (mixingand/or reaction) element in pipe configurations. Flow input channels 1and 2 are for the separate fluids which will be mixed. Additional inputscan be added if more than two fluids are to be mixed. Input 1 providesflow to offset fractal distributor 7 while input 2 provides flow tooffset fractal distributor 6. The fluid flows are scaled and distributedthrough these offset fractals.

[0039] After independent fractal scaling of the fluids, the two inputflows contact one another through merging channels 8 and proceed in amixed condition through channels 9. In the channels 9, hereinafterdenominated “contact channels,” the fluids are finally brought intocontact one with another. The flows in contact channels 9 are re-scaledto a single flow through fractal collector 10 and exit channel 3. Theenclosure 11 is used if temperature control is required for mixing orreaction or if an enclosure is needed for flanging or other attachment.In the case of temperature control, a heat exchange fluid is typicallypassed from conduit 4 to the inside volume of the mixer for heatexchange with the internal conduit and out conduit 5. In the case ofusing the enclosure as an attachment structure, enclosure 11 can be asolid material surrounding the internal channels. For example, enclosure11 can be used as a simple flange for attachment to a pipe flange.

[0040]FIG. 2 illustrates the offset of fractal distributors 6 and 7. Thefractal distributors do not intersect because they are set on differentplanes, as shown in FIG. 3. Note that the flows through fractals 6 and 7are independent and cannot contact one another until after they exitfractals 6 and 7. If more than two fluids are mixed, additionalindependent offset fractals can be used.

[0041] If more than two fluids are mixed or reacted by these devices,all can be merged simultaneously or they can be progressively mixed.This can easily be accomplished by placing merging channels at differentpositions along the length of the device. An example of such a use wouldbe when two fluids must first be mixed or reacted before mixing orreacting with a third fluid. The third fluid would merge at anappropriate distance downstream from the merging of the first twofluids.

[0042] For purposes of illustration, each input conduit is shown scaledto 64 smaller conduits. However it is a basic characteristic of thisdevice that the fractal conduits can be progressively bifurcated tosmaller and more numerous paths until restrictions on manufacturing arereached. It is recognized that increasing the number of bifurcationswill provide a progressively improved homogeneity of mixing andreaction. Because each independent distribution fractal (6 and 7) inthese figures bifurcates to 64 flow paths, there are 128 totaldistribution channels prior to merging and these merge to form 64contact channels (9). FIG. 3 illustrates the approximate location offractal collector 10.

[0043] Because this invention uses fractals for the offset structures,those skilled in the art will recognize that this provides an inherentgeometric variability which adds to the practical value of thisinvention. One reason variable geometry may be desired for the fractalsis that the device may require a geometry constrained by thecorresponding geometry of an enclosure it is contained in or a receivingdevice it exits into. Another reason for variable geometry is to providethe artisan with control over hydraulic characteristics such as pressuredrop.

[0044] Fractals are constructed using an initiator structure, or parentstructure, with self similar structure added at smaller and smallerscales. The initiator in the illustrated embodiment is in the form of an“H” and as a result, four new child structures are added to each “H” assmaller scale structure is added. It is well known in the art thatfractals can be constructed using variations in the initiator geometry,number of branches, branch angles and in the amount of initiatorsymmetry. Just as an example, the initiator could be a symmetric “Y”having one leg longer that the other two.

[0045] Another way to vary the device geometry is by altering the childstructures. The child structures need not exhibit scaled-down geometryidentical to the initiator. This type of variation can include thegeometry or symmetry of the child structures at each iteration, forexample by using variable scaling factors for determining childstructure dimensions and channel diameters.

[0046] We note that the number of generations of child structure can bevaried as desired (the number of fractal iterations) to obtain a desiredlevel of scaling prior to mixing/reaction or to meet practicalrequirements such as the avoidance of device plugging.

[0047] The offset fractals need not be identical. As an example, ifthree offset fractals are used to mix or react three materials, two ofthe fractals could of an identical geometry while a third is not, or allthree could be of different geometry. The reason for this is that thematerials to be treated may have variable characteristics which wouldsuggest to a person skilled in the art to use different geometries. Forexample, the flow rate through one fractal may be very high comparedwith a second so that pressure drop may be best controlled by usingdiffering channel cross sectional area or number of fractal iterationsthrough each individual fractal.

[0048]FIG. 4 is a top view and FIG. 5 is an isometric view of the pipeelement embodiment. While this embodiment is useful when the flow fromthe mixing or reactor process should be re-collected into a single flow,the device can be used to advantage without the collector. This can beuseful, for example, when mixing air and gas for a combustionapplication or for injecting the mixture into the side of a tank orother vessel. FIG. 6 illustrates an embodiment without re-collection. Inthis case the fluids from inputs 1 and 2 are scaled and distributed inthe same manner as described earlier but the flows are not re-collectedinto one flow, i.e., output channel 3 and fractal collector 10 have beenremoved. In this embodiment the large number of contact channels 9 exitthe device independently at contact channel exits 12. Because the restof the device is the same as described earlier, in this example therewill be 64 such exits.

[0049] It is also possible to eliminate the merging channels 8 andmixing channels 9 so that the scaled and intermingled flows exit thedevice prior to contact with one another. FIG. 7 illustrates thisminimal configuration for the invention and consists of the flow inputs1 and 2, and the offset fractals 6 and 7. Fractal 7 exits throughoutlets 13 and fractal 6 exits through outlets 14.

[0050] For these last two embodiments, the enclosure (11) is againoptional but can be useful for either heat exchange or for attaching orflanging the device to a vessel.

[0051] We note that the area that the offset fractals exit into need notbe a plane. The fractals can exit to a curved or irregular surface. Thiscan be useful, for example, if the target vessel has a curved orirregular shape. In such a case, it can be useful to match the curvedsurface of the vessel with a complementary curve on the exit surface ofthe mixing device.

[0052] The figures show the offset fractals bifurcated perpendicular tothe large scale inlet and outlet flow direction. It is possible tobifurcate the fractals at any angle from perpendicular to nearlyparallel to these flow directions. Configuring at angles which are notperpendicular to the large scale flow can have advantages as well asdisadvantages. One advantage of using fractal bifurcations more in-linewith the flow direction is that it may be possible to operate the devicewith less pressure drop since flow momentum will not be forced to makeas drastic a change in direction as the bifurcations are-carried out. Adisadvantage can be that the device will become longer in the directionof the flow and perhaps less compact. It is therefore a user decisionwhich advantages are most important for a given process and from theseconsiderations chose the appropriate bifurcation angles.

[0053] This invention uses two or more offset fractals whichindependently scale fluids before they contact one another. The methodof offset scaling can be different than in the figures. For example, theseparate fractals can be contained within one another. A smaller conduitcarrying one fluid can be placed inside a second larger conduit. Asecond fluid can therefore flow between the inner surface of the largerconduit and the outer surface of the smaller inner conduit. The twoconduits can progressively be bifurcated to smaller and smaller scaleuntil a desired exit size is reached. As with the above embodiments, theflows can be merged, in this case by simply ending the inner conduit sothat the inner flow contacts the outer flow. The merged flows can alsobe collected and further merged into a single flow, if desired, asdescribed earlier. Note that we are defining “offset” to include smallerconduit inside of larger conduit since the flows are properly keptoffset from one another by this optional method.

[0054] This method of offsetting fractal conduits within one another canbe extended to any number of separate fluids by adding a separateenclosed conduit for each fluid.

[0055] We note that in the event of operation with fluctuating pressuresbetween the independent flows or in the event that a particular flow istemporally shut off it can be useful to have check valves on channels toavoid backflow of one fluid through the distribution fractal of adifferent fluid.

[0056] This invention can be applied over the entire range of fluidprocessing scales from very small scale applications to very large scaleindustrial use. The reason for this is that the fractal structures usedin this invention provide a continuing scaling function as applicationscale changes. This wide range of applicability is one of the inherentadvantages of this mixer design.

[0057] Because this device is used for mixing and/or reaction of fluids,the resulting products can be used as desired in subsequent processingequipment.

[0058] It is noted that a particular manufacturing technique is notrequired to realize this invention. Computer aided machining,stereolithography, photochemical etching, laser cutting, molding,micro-machining, nanotechnology, ion deposition and conduit constructiontechniques are a few appropriate methods for building these devices.

[0059] It is recognized that future manufacturing techniques which mayimprove the ability to construct small scale structure will also beuseful for construction of these devices.

What is claimed is:
 1. A structure for mixing at least two fluids, said structure comprising: at least two fluid transporting fractals, each said fractal having a respective fluid input which bifurcates to a plurality of fluid outputs, said fractals being positioned to be offset from one another, each fractal being configured to facilitate an independent flow therethrough, said fluid exits from the separate offset fractals being configured such that they are homogeneously interspersed with one another, and said fluid outlets being disposed such that fluid exiting said outlets flows across an area.
 2. The structure of claim 1 wherein the flows exiting said outlets of said offset fractals are merged with corresponding exiting flows from the other offset fractals into an array of mixed flows.
 3. The structure of claim 2 wherein the said array of mixed flows is further merged into a single flow.
 4. The structure of claim 3 wherein the said merging to a single flow is accomplished by using a fractal arrangement wherein the direction of flow is from the small scale end of the fractal arrangement to the large scale end of the fractal arrangement.
 5. The structure of claim 1 wherein at least some of the flows are retained within flow channels disposed in a surrounding enclosure such that a heat exchange fluid can pass over the outside surface of the enclosed flow channels.
 6. The structure of claim 1 wherein at least some of the flow channels are surrounded by an enclosure such that the enclosure can be used for attaching the structure to a support structure.
 7. The structure of claim 1 wherein at least some of the flows are retained in flow channels, said flow channels being surrounded by an enclosure such that the enclosure provides support for the flow channels. 